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MELCOR 2.1 Leak Path Factor Assessment and Guidance

MELCOR 2.1 Leak Path Factor Assessment and Guidance. David L.Y. Louie dllouie@sandia.gov. LPF Application of MELCOR.

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MELCOR 2.1 Leak Path Factor Assessment and Guidance

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  1. MELCOR 2.1 Leak Path Factor Assessment and Guidance David L.Y. Louie dllouie@sandia.gov

  2. LPF Application of MELCOR • MELCOR is being developed by SNL for the Nuclear Regulatory Commission (NRC). Details about the development of MELCOR from the previous MELCOR presentation were discussed in this workshop . • Even though MELCOR is developed for reactor applications, but because of the modular in nature, a user can select certain modules (packages) to be used in LPF applications. • MELCOR is a DOE Toolbox Code for LPF applications • DOE nuclear and nonnuclear facilities for many years • MELCOR 1.8.5 is designated version (which is an obsolete) • Many users have used MELCOR 1.8.6, but requires additional validation and verification procedures • MELCOR 1.8.6 is unsupported by SNL, so that much of the effort can be devoted to the development of MELCOR 2.0 and beyond.

  3. Code Version Differences • FORTRAN language has been used in the life of the MELCOR code development; however, beginning with Version 2.0, the version of FORTRAN has been switched from FORTRAN77 to FORTRAN95 to ensure future developments in terms of extensibility and maintainability. • Beginning with Version 2.0, there is a significant change in the code architecture, even though most the 1.8.6 algorithms were kept intact. • The original Version 2.0 was developed using the object-oriented approach in terms of input and calculated variables, which contributes the input format changes beginning with this version. • The new input format utilizes the “block input” approach in different levels of inputs: program[MELGEN, MELCOR], packages[CVH, FL, etc.], and objects [CV_ID, etc.] .

  4. Switching to MELCOR 2.1 • Some re-training may be required for using the “block input” approach for the MELCOR 1.8.6 users. • Easy-to-use converter, which allows the decks developed in Version 1.8.5 without the “COR” package, and Version 1.8.6 to be converted into MELCOR 2.1. • Symbolic Nuclear Analysis Package (SNAP) developed by Applied Programming Technology, Inc. for NRC • There is a plug-in for MELCOR • The use of SNAP requires a license agreement with NRC • Some users may find CVH thermodynamic input difficult to use. To help this, an alternative Input, CV_THERM, restores some of the Version 1.8.6 features.

  5. Assessments • The assessment task is in progress at SNL – Volume III (Demonstration Problems) of the manual is being developed. • Appendix A of this manual devotes for the non-reactor application • This appendix addresses a finding for MELCOR with the gaps analyses conduced by DOE in 2004, which indicated inadequate sample problems for LPF specific cases. • Much of the thermal hydraulics and aerosol physical models of MELCOR are assessed using experiments tailored for reactor applications. • For LPF applications, we try to verify the MELCOR results from the previously reported calculations done, such as those results reported in the DOE MELCOR guideline report, and other reports, such as from LA-UR-03-7945 by Jordan and Leonard.

  6. MELCOR LPF Results (%)* from MELCOR Guidance Report *1.8.5 is calculated using the official release version RL, 1.8.6 is calculated using the official release version YV 3404, and 2.1 is calculated using revision 1570.

  7. MELCOR Results –Example 3 of LA-UR-03-7945# #LA-UR-99-2513 (C. Shaffer and M. Leonard) *1.8.5 values are using the official release version RL, 186 values are calculated using the official release version YV 3404, and 2.1 values are calculated using official release version RL NL 4261. **1.8.5 reported values from Table 4-2 of LA-UR-03-7945

  8. Useful Features in MELCOR 2.1 • Physical Models: • Counter-current flow model (FL_CCF card) – allows coupling of two paths through momentum exchange using Epstein-Kenton correlations – mainly for natural circulations • Benchmark against CFD code • Can be used to address the counter-current exchange of combustion gases through open doorway in a fire scenario • Turbulent aerosol deposition model (RN1_TURB) [optional input] – models the aerosol deposition in pipes or ducts -the turbulent flow regime. (cautions should be placed when applying this model for the LPF applications, because the benchmark is done for the reactor accident conditions)

  9. Useful Features (continued) • Enhance Features: • Aerosol deposition deactivation flag (RN1_ADFG card) [optional input] – allows to switch off deposition models, such as gravitational, thermophoresis and diffusive settling • Filter model – flexible enough to permit the user to model a variety of aerosol or vapor deposition, flow and degradations in filters – via control functions • Spray model – Because of the generality of the spray inputs, the spray model can be used to simulate the fire sprinkler system – reduce thermal condition of the accident and to scrub radionuclides/aerosols to minimize the LPF value.

  10. Useful Features (concluded) • Utility Features: • Common block feature “(((name block” and ending with “)))” can be used to allow a single input file to simulate a number of different runs, especially good for sensitivity studies. • ResultsReviewer Utility, in conjunction of the RN input (RN1_VISUAL) to provide a way to study the aerosols • Example – Appendix E in the MELCOR Guidance Report – Simulation for the V300 adjacent to the room with the fire and aerosol release. • SNAP simulation – Appendix C sample in the MELCOR Guidance Report – aerosol fraction display, with evacuation door simulated.

  11. Conclusions MELCOR 2.x represents the latest version of MELCOR, which should be used by the safety basis community for the LPF applications. Assessments of this current code version show results that are consistent with MELCOR 1.8.5, the current DOE Toolbox code. With the enhancements to be included in this code version and beyond, the safety analyst should be benefited.

  12. Future Development of MELCOR • Desired improvement: • Hot gas layer modeling for simulating fire scenarios should be added. • Currently MELCOR only models deflagration of hydrogen and carbon monoxide, combustion of other solid, liquid and gas (including user-defined type) should be added. • MELCOR may be used in the development of a fuel reprocessing source term analytical tool for NRC • Empirical correlations for aerosol generation size/mass and wall failure phenomena from liquid explosions and liquid criticality events • Additional development model may be included in the effort that could be benefited for the DOE safety basis community for the LPF applications.

  13. Questions?

  14. SNAP Interface return

  15. Example 3 of LA-UR-03-7945 Brief Description Nodalization: 55 CV multi-level problem • Fire occurs in the lab • Source: 1 g PuO2 • Sensitivity Studies • Leakage – door gap size • Wind speed • Smoke • Filter efficiency Referenced from LA-UR-99-2513 (C. Shaffer and M. Leonard) RETURN

  16. Thermodynamic Input Options RETURN

  17. Typical SNAP Conversion RETURN IMPORT input file (version 1.8.5 without COR or version 1.8.6) Selected version to be converted (i.e., 2.1) Export input file

  18. Nodalization of Appendix E Sample RETURN

  19. Reactor Hot Leg Natural Circulation NUREG-1922 RETURN

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